Math-model based gear -shift control strategy for advanced vehicle powertrain systems.

Abstract

As vehicle powertrain systems become more and more complex with the integration of advanced technologies (e.g., electronic throttle control, variable displacement), it is becoming ever so difficult to obtain an optimal gear-shift control strategy using the current practice since it is frequently based on the experience and know-how of the calibration engineers and tuned in a heuristic manner. To overcome the short comings of the current practice, a math-model based design procedure based on the dynamic programming method is developed to generate optimal control strategy for vehicle powertrain systems. This computer-based procedure can accelerate the design process and achieve guaranteed performance level. Moreover, it is re-usable and more flexible that it can be applied to various configurations of the powertrain system with more advanced components. To illustrate the design procedure in detail, the gear-shift control of a vehicle with conventional powertrain system (i.e., 4-speed AT and engine) was optimized for best fuel economy while satisfying a prescribed drivability requirement using step throttle launching maneuvers. The resulting gear-shift map achieved better drivability and fuel economy than the current production map of the target vehicle. Also, the development time for a gear-shift map was significantly reduced (days vs. months). Then, based on this procedure, simultaneous control of the throttle and the gear of a powertrain system with Electronic Throttle Control (ETC) were optimized. The resulting throttle/gear map satisfied the driver's demand (power) in a more reliable and efficient way. Also, optimal gear control strategy was investigated for powertrain systems with variable displacement technology. These case studies showed the flexibility of the design procedure where it can be used for any combination of the powertrain system. In addition, dynamic programming is used to optimize the powertrain system following a fuel economy test drive cycle. This concept can be used to evaluate the fuel efficiency of new powertrain technologies and/or various configurations of the powertrain system as a technology assessment tool. The proposed design procedure was found to be more efficient (better result in much less time) in producing an optimal gear control strategy. It also proved to be flexible and can be applied to more advanced powertrain systems with unconventional configurations, which the current practice is not able to handle.